Method for manufacturing carbon nanotubes

ABSTRACT

The present invention provides a method for manufacturing carbon nanotubes. The method includes the following steps: (a) providing a substrate ( 3 ); (b) depositing a catalyst material ( 1 ) onto the substrate; (c) exposing the catalyst material to a carbon containing gas for a predetermined period of time in a predetermined temperature such that an array of carbon nanotube having a predetermined length grows from the substrate in a direction substantially perpendicular to the substrate; (d) removing the carbon nanotubes from the substrate; and (e) dispersing the carbon nanotubes via ultrasonication in a dispersant, the dispersant being ethanol or 1-2 dichloroethane. The carbon nanotubes of the present invention have a predetermined same length and are aligned parallel to each other.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for manufacturing carbon nanotubes, and more particularly to a method for manufacturing carbon nanotubes having a predetermined same length.

[0003] 2. Description of Related Art

[0004] Carbon nanotubes have shown many unique electrical and mechanical properties. Their potential applications include use in field emitters, gas storage and separation, nanoprobes, chemical sensors and high strength composites. Currently there are three principal techniques to manufacture high quality carbon nanotubes, namely arc discharge, laser ablation and chemical vapor deposition. The carbon nanotubes made by arc discharge and laser ablation are often accompanied by a large volume (up to 50%) of contaminants and are tangled with each other. It is very difficult to separate the carbon nanotubes. Furthermore, those production techniques are capital-intensive and are likely limited to research quantities. The carbon nanotubes made using a chemical vapor deposition technique are in good yield—occasionally over 90%—and have few contaminants.

[0005] Carbon nanotubes having a predetermined same length and being parallel to each other are generally desired in field emission devices, in composite reinforced material and in electrovacuum device. However, not all methods can directly produce carbon nanotubes having a predetermined same length and being parallel to each other.

[0006] Therefore, a method for manufacturing carbon nanotubes having a predetermined same length and being parallel to each other is desired.

SUMMARY OF THE INVENTION

[0007] Accordingly, an object of the present invention is to provide a method for manufacturing carbon nanotubes that have a predetermined same length and that are aligned parallel to each other.

[0008] In order to achieve the object set forth above, the present invention provides a method for manufacturing carbon nanotubes. The method comprises the follows steps:

[0009] (1) depositing a catalyst material onto a substrate;

[0010] (2) exposing the catalyst material to a carbon containing gas for a predetermined period of time at a predetermined temperature such that an array of carbon nanotubes having a predetermined length grows from the substrate in a direction substantially perpendicular to the substrate; and

[0011] (3) removing the carbon nanotubes from the substrate.

[0012] Other objects, advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic view of depositing a catalyst material onto a substrate in accordance with the present invention;

[0014]FIG. 2 is a schematic view of an annealed catalyst material on a substrate in accordance with the present invention;

[0015]FIG. 3 is a schematic view of growing an array of carbon nanotube on a plurality of substrates in accordance with the present invention;

[0016]FIG. 4 is a schematic view of removing the carbon nanotubes from one of the substrates of FIG. 3 in accordance with the present invention;

[0017]FIG. 5 is a transmission electron microscope image of an array of carbon nanotubes in accordance with the present invention after treatment by ultrasonitication in a dispersant;

[0018]FIG. 6 is a transmission electron microscope image of the array of carbon nanotubes in accordance with the present invention after treatment by ultrasonication in a dispersant, wherein the carbon nanotubes of the array are separated; and

[0019]FIGS. 7, 8, 9 and 10 are respectively arrays of carbon nanotube having different lengths in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0020] The present invention provides a method for manufacturing carbon nanotubes that have a predetermined same length and that are aligned parallel to each other. The method comprises steps as follows:

[0021] (1) referring to FIG. 1, providing a substrate 3 comprising a wafer silicon or silica;

[0022] (2) depositing a catalyst material 1 onto a surface of the substrate 3 by electron beam evaporation, sputtering or coating, such that a catalyst material film 11 between 4-10 nm thick is formed on the surface of the substrate 3, the catalyst material 1 being selected from the group consisting of iron, nickel and cobalt;

[0023] (3) referring to FIG. 2, annealing the catalyst material film 11 in air at 300-500 degrees Centigrade for between 8-12 hours, such that the catalyst material film 11 is changed into separate nanoparticles 12;

[0024] (4) referring to FIG. 3, putting a plurality of the substrates 3 with nanoparticles 12 in a furnace 4;

[0025] (5) heating the furnace 4 to between 600-1000 degrees Centigrade in flowing protecting gas (not labeled), the protecting gas being selected from the group consisting of argon, nitrogen and helium;

[0026] (6) introducing a flow of carbon containing gas into the furnace 4 for between 15 seconds and 40 minutes, the carbon containing gas being selected from the group consisting of acetylene, methane and ethylene;

[0027] (7) growing an array of carbon nanotubes 5 (see FIG. 4) having a predetermined length from the surface of each substrate 3;

[0028] (8) cooling the furnace 4 to room temperature, and taking the substrates 3 out from the furnace 4;

[0029] (9) referring to FIG. 4, removing the carbon nanotubes 5 from the array of each substrate 3 by using a blade 6; and

[0030] (10) dispersing the carbon nanotubes 5 via ultrasonication in a dispersant, the dispersant being ethanol or 1-2 dichloroethane.

[0031] Referring to FIGS. 5 and 6, since the carbon nanotubes 5 of the array are substantially parallel to each other, a multiplicity of separate carbon nanotubes 5 can be easily obtained after ultrasonication in the dispersant.

[0032] Referring to FIGS. 7, 8, 9, and 10, the predetermined length of the carbon nanotubes 5 can be obtained by controlling reaction conditions such as a time of reaction and a temperature of reaction.

EXAMPLE 1

[0033] growing a carbon nanotube array of 10 microns height on each of a plurality of silicon wafers. An iron film of 5 nm thickness is deposited on a porous surface of each silicon wafer. The porous surfaces of the silicon wafers are obtained by electrochemical etching of P-doped N⁺-type silicon wafers. The silicon wafers are then annealed in air at 400 degrees Centigrade for 10 hours. This annealing step oxidizes the iron film to create a largely iron oxide nanoparticles. The silicon wafers are then placed in a cylindrical quartz boat sealed at one end, and the quartz boat is put into the center of a 2-inch quartz tube reactor housed in a tube furnace. The furnace is heated to 690 degrees Centigrade in flowing argon. Ethylene is then introduced into the furnace for 15 seconds, after which the furnace is cooled to room temperature.

EXAMPLE 2

[0034] growing a carbon nanotube array of 100 microns height on each of a plurality of silicon wafers. An iron film of 5 nm thickness is deposited on a porous surface of each silicon wafer, similar to that described above in relation to Example 1. The substrates are then annealed in air at 400 degrees Centigrade for 10 hours. The substrates are placed in a cylindrical quartz boat sealed at one end, and the quartz boat is put into the center of a 2-inch quartz tube reactor housed in a tube furnace. The furnace is heated to 690 degrees Centigrade in flowing argon. Ethylene is then introduced into the furnace for 5 minutes, after which the furnace is cooled to room temperature.

EXAMPLE 3

[0035] growing a carbon nanotube array of 500 microns height on each of a plurality of silicon wafers. An iron film of 5 nm thickness is deposited on a porous surface of each silicon wafer, similar to that described above in relation to Example 1. The substrates are then annealed in air at 400 degrees Centigrade for 10 hours. The substrates are placed in a cylindrical quartz boat sealed at one end, and the quartz boat is put into the center of a 2-inch quartz tube reactor housed in a tube furnace. The furnace is heated to 710 degrees Centigrade in flowing argon. Ethylene is then introduced into the furnace for 10 minutes, after which the furnace is cooled to room temperature.

[0036] It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. 

What is claimed is:
 1. A method for manufacturing carbon nanotubes comprising steps as follows: (1) providing a substrate; (2) depositing a catalyst material onto the substrate; (3) exposing the catalyst material to a carbon containing gas for a predetermined period of time at a predetermined temperature such that an array of carbon nanotubes having a predetermined length grows from the substrate in a direction substantially perpendicular to the substrate; and (4) removing the carbon nanotubes from the substrate.
 2. The method in accordance with claim 1, further comprising dispersing the carbon nanotubes via ultrasonication in a dispersant after step (4).
 3. The method in accordance with claim 1, wherein in step (1) the catalyst material is selected from the group consisting of iron, cobalt and nickel.
 4. The method in accordance with claim 3, wherein step (2) comprises depositing a catalyst material film between 4 and 10 nm thickness on the substrate and annealing the catalyst material film at between 300-500 degrees Centigrade for between 8-12 hours such that the catalyst material is changed into separate nanoparticles.
 5. The method in accordance with claim 1, wherein in step (3) the predetermined temperature is between 600-1000 degrees Centigrade.
 6. The method in accordance with claim 5, wherein in step (3) the carbon containing gas is selected from the group consisting of ethylene, methane and acetylene.
 7. The method in accordance with claim 5, wherein step (3) further comprises flowing protecting gas before exposing the catalyst material to the carbon containing gas.
 8. The method in accordance with claim 1, wherein step (3) comprises exposing the catalyst material iron to ethylene at 690 degrees Centigrade for 15 seconds such that a carbon nanotubes array of 10 micron height grows from the substrate in a direction substantially perpendicular to the substrate.
 9. The method in accordance with claim 1, wherein step (3) comprises exposing the catalyst material iron to ethylene at 690 degrees Centigrade for 5 minutes such that a carbon nanotubes array of 100 micron height grows from the substrate in a direction substantially perpendicular to the substrate.
 10. The method in accordance with claim 1, wherein step (3) comprises exposing the catalyst material iron to ethylene at 710 degrees Centigrade for 10 minutes such that a carbon nanotubes array of 500 micron height grows from the substrate in a direction substantially perpendicular to the substrate.
 11. The method in accordance with claim 1, wherein in step (4) the carbon nanotubes are removed from the substrate by using a blade.
 12. The method in accordance with claim 2, wherein the dispersant is select from ethanol or 1-2 dichloroethane.
 13. A method for manufacturing carbon nanotubes comprising steps as follows: (1) providing a plurality of substrates in a furnace; (2) depositing a catalyst material onto each of the substrates; (3) exposing the catalyst material to a carbon containing gas for a predetermined period of time at a predetermined temperature such that an array of carbon nanotubes having a predetermined length grows from the substrate in a direction substantially perpendicular to the substrate; and (4) removing the carbon nanotubes from the substrate.
 14. The method in accordance with claim 13, wherein said substrates are upwardly obliquely arranged along a lengthwise direction of the furnace and in a parallel relation with one another, and commonly facing toward an entrance of the furnace where the gas comes in. 